The name and use of PAG quenching media for fasteners

PAG is an abbreviation for English names. There are three ways to write PAG in English. See Table 1 for details.

English name Chinese translation Poly alkylene glycol Polyethylene glycol, polyoxyalkylene, polyalkylene glycol, polyglycol Poly alkylene glycol ether polyether, Polyglycol ether Polyoxyethylene-propylene polyether Polyoxyethylene, propylene polyether Table 1PAG Names in Chinese and English


Due to the confusion of Chinese translation, especially the translation to polyethylene glycol is not standardized because polyethylene glycol (PEG) is already in Chinese. So why not translate it to PAG? PAG is a copolymer of polyoxyethylene and polyoxypropylene. Adjusting the ratio of the two, the reversal point of 70-88°C can be obtained. Inversion phenomenon refers to: As the temperature rises, the solubility decreases, so it is called inversion. When a certain temperature is reached, the solute begins to precipitate out of the solution. This temperature is called the inversion point. Due to the presence of reversed solubility, when working in quenching, after the steam film stage and boiling stage, the liquid temperature around the workpiece is higher than the inversion point, PAG precipitates and forms a PAG solute film on the surface of the workpiece. The higher the PAG concentration, the thicker the membrane and the poorer the ability of the solution to absorb heat from the workpiece. This is the mechanism by which the PAG reduces the cooling capacity in the low temperature zone. That is, by controlling the concentration of the PAG, the thickness of the PAG solute film can be controlled, thereby obtaining an ideal cooling capacity in the low temperature zone.

The main cause of quench cracking of fasteners is rapid cooling at the point where the steel starts to undergo martensitic transformation (MS) and below this temperature range. For this reason, the water-soluble quenching medium usually represents the cooling characteristics of the quenching liquid as the cooling rate when the part is cooled to 300°C. Considering that most of the high-strength fasteners use medium-carbon structural steels whose MS point is near 300°C, PAF quenchants such as Houghton AQ251 are selected. In short, it has a low cooling rate at 300°C, and its ability to prevent bolts from quenching is strong. At 300°C, the cooling rate is high, and its hardenability is also high. Of course, bolts tend to crack. The use of PAG quenching fluid is characterized by adjustable cooling characteristics and easy measurement and control of concentration. Because the liquid temperature has a great influence on the cooling performance, when using the PAG quenching liquid, a complete circulation cooling system should be provided so that the liquid temperature below 50° C. can be adjusted for normal use during use. When the concentration is constant, the cooling rate decreases as the temperature of the liquid increases. In order to obtain the consistent quenching and cooling effect as possible, the temperature of the quenching medium should be controlled within a narrower range of 25°C to 35°C. If it is difficult to strictly control the liquid temperature due to the weather, the quenching can also be adjusted by changing the concentration. Cooling speed. For example, in summer, when the temperature is high, the cooling system cannot temporarily reduce the temperature of the quenching liquid to the specified range, and it can add some tap water to it to increase the quenching cooling rate. In winter, when the liquid temperature is too low, the high temperature steam can be used to heat the quenching liquid or pass through. Increase the concentration to reduce the quench cooling rate.

Some carbon structural steels with a carbon content of less than or equal to 0.20%-0.35% are quenched and hardened with poor hardenability and simple shapes such as bolts and nuts . Tap water can often be used, which can save production costs. As a quenching medium, the cooling characteristics of tap water are: the workpiece cools rapidly when it is in the high temperature stage, and it cools quickly when the workpiece is in the low temperature stage, and the cooling rate can make the hardenability poor and the large-size fasteners harden. , And get a deeper hardened layer, which is the advantage of tap water. However, quenching with tap water has three major disadvantages: the first is that the cryogenic cooling is too fast, which makes most steels and bolts prone to quench cracking; the second is that the bolts are cooled too quickly in the low-temperature stage, and the slender specifications and thin parts are easy to enter because of water Improper way to quench deformation. The third and disadvantage that many people easily overlook is that as the water temperature rises, the quenched and cooled steam film stage will gradually increase, and the cooling rate when the workpiece is in the low temperature stage will gradually decrease. For this reason, small-size bolts, When the nuts are stacked densely and put into water quenching, the water temperature of the bolts placed outside is low, and the water temperature of the bolts stacked inside is high, so that the external bolts are subjected to rapid cooling, high hardness after quenching, and easy to quench and crack. The studs piled inside are subjected to slow cooling, low hardness after quenching, and the denser the stacking of bolts, the less smooth the flow of water during quenching, the greater the difference.

When tap water is used as the quenching medium, it is advisable to avoid weaknesses and try to control the water temperature. Generally, the temperature should be 15°C to -30°C. The strong quenching medium can be used to promote the smooth passage of the quenching medium from the bolts to reduce the temperature difference between the internal and external water. Function forumhottag_callback(data){ tags = data; }